(i) Field of the Invention
The present invention relates to a musical sound signal generation apparatus, particularly to an apparatus which can effectively utilize a musical sound generation channel.
(ii) Description of the Related Art
For example, an electronic keyboard instrument represented by an electronic piano includes a musical sound signal generation apparatus. The apparatus is provided with: a plurality of musical sound generation channels; a channel state storage unit for storing the operation state of each musical sound generation channel; an assigning unit for, when a key-on is detected, referring to the storage content of the channel state storage unit to select a pair of musical sound generation channels, assigning a left musical sound signal for stereo performance to one of the selected musical sound generation channels which is an L channel, and assigning a right musical sound signal for the stereo performance to the other channel which is an R channel; a left output system for outputting the left musical sound signal; and a right output system for outputting the right musical sound signal. A left speaker is driven in response to the musical sound signal from the left output system, and a right speaker is driven in response to the musical sound signal from the right output system so that the stereo performance is realized.
To realize the stereo performance, two musical sound generation channels (L/R channels) are necessary for one key operation (key-on). If the pairs of L/R channels are prepared for the number of keys, a shortage of channels is not caused. However, the increasing of the number of the musical sound generation channels increases costs. Therefore, a technique of suppressing the number of musical sound generation channels to some degrees (e.g., 32 channels), and effectively utilizing a limited number of musical sound generation channels has been researched.
As one of such techniques of effectively utilizing the musical sound generation channels, a musical sound signal generation apparatus is disclosed in Japanese Patent Application Laid-Open No. 49159/1998. In this musical sound signal generation apparatus, when a new key-on is made during use of all the musical sound generation channels, two pairs of L/R channels are selected, one of the musical sound generation channels constituting the pair is truncated (rapidly attenuated), and the remaining channel is allowed to operate as it is. Thereby, since two musical sound generation channels become vacant, they can be used as the L/R channels for the key subjected to the new key-on.
In the technique of the Japanese Patent Application Laid-Open No. 49159/1998, however, since only the sounding of one-side channel remains out of stereo sounding, sound volume balance is lost on the left and right. To prevent this, the channel to be truncated needs to be controlled so that since the L channel was truncated the last time, the R channel is to be truncated this time. Such complicated control is necessary.
Moreover, the sounding of the one-side channel is completely eliminated by the truncation processing. For example, when the key-on is successively made with a damper pedal stepped on, the total sound volume is desired to gradually increase. However, the total number of channels cannot be increased to obtain the stereo sound volume or more volume.